Besides the BRCA-genes, mutations occur in other genes that protect the individual from cancer development. Usually, these mutations have lower penetrance, which means that there is a lesser chance of developing cancer from these mutations. One of the most studied mutations besides BRCA-1 and BRCA-2 is the CHEK2-gene variant. CHEK2 is a gene located on chromosome 22, that encodes for a protein helping us to repair damaged DNA. A mutation in the CHEK2-gene inherited from one of the parents increases the breast cancer risk 2-fold. However, if the mutation exists in both the paternal and maternal inherited genes, the risk increases 6-fold. The gene mutation seems to be more frequent in the northern European populations, with 3% of people carrying the mutation (Finish, Dutch), than in southern European populations (0.5%). Although more rare than the BRCA-mutations, and incorporating a lesser risk for breast cancer, CHEK2 is currently considered the third most important breast cancer susceptibility gene.
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